10 ohm 25W resistor isn’t really adequate protection for shorts. In short situation the current will be 2.4A and power will be 58W (if the supply transformer can supply that much current). It can probably survive the overpower but will be REALLY hot. The supply transformer may be damaged from overload and the heat may damage things. Better to put in some sort of electronic current limit at a convenient level for a couple valves energized at the same time. If you have a system needing a very large number of zones at the same a more complex system would be needed but that’s an uncommon situation.